PROJECT SUMMARY Not all autoreactive B cells are censored by central tolerance during their development. Thus, mechanisms of B cell anergy are essential for the functional silencing of autoreactive B cells that exist in the periphery in both humans and mice. However, it remains unclear why this poorly defined process of immunological tolerance allows for the temporary retention of autoreactive B cells in the periphery given that, under certain genetic and environmental settings, these cells can contribute to autoimmunity. Indeed, anergic B cells can be released from their functionally inert state but requires unique circumstances (e.g., strong TLR stimulus and highly multimerized antigen), which could presumably occur during an uncontrolled infection. As such, we propose that autoreactive anergic B cells may serve as a reserve population able to respond to pathogens not contained by an initial immune response and particularly for pathogens that aim to evade the immune response through molecular mimicry of self-antigens. Accordingly, work from our lab has recently evaluated if autoreactive B cells that are normally silenced by immune tolerance can contribute to a protective cross-reactive antibody response. To accomplish this we used both autoimmune prone B6.Sle123 mice and wild-type mice treated with pristane, a treatment characterized to impair tolerance and promote autoantibody production. These mice were immunized with HIV envelope protein (Env) and immune sera was found to neutralize tier 2 genetic subtypes of clinically relevant HIV-1, a pathogen proposed to exploit immune tolerance in order to evade the immune response. Furthermore, from these mice we isolated Env-specific neutralizing monoclonal antibodies that also recognize the H2A histone protein. Thus, the goal of this proposal is to use mouse and humanized mouse models to identify the nature and mechanisms that facilitate this antibody response by peripheral autoreactive B cells and to establish conditions that experimentally breach tolerance and promote cross-reactive autoantibody responses by anergic B cells.